ref(server): make idle time of a http connection configurable

[Dav1dde]

With the idle time configurable we can prevent a pile up of open connections which never see any activity.

See also on the hyper issue tracker:

https://github.com/hyperium/hyper/pull/3743
https://github.com/hyperium/hyper/issues/1628
https://github.com/hyperium/hyper/issues/2355
https://github.com/hyperium/hyper/pull/2827

[jjbayer]

Would this work with a single variable deadline: Instant, i.e. let Poll::Ready reset the deadline to a point in the future and Poll::Pending check it?

Is the usage of a timer + boolean an optimization to reduce calls to Instant::now()?

[Dav1dde]

It does reduce the amount of instants created and I also wanted the timer to only start when you poll a Pending. I initially had a Option<Sleep> implementation, but that re-created the Sleep a bunch which is especially expensive with the Box::pin. In the end that's the approach I liked most.

[jjbayer]

Not sure if this would make typing annoying, but it would be cool if timeout was non-optional here. So if there's no timeout set in the config, don't use IdleTimeout.

[Dav1dde]

That works if we instead use Box<dyn AsyncRead + AsyncWrite + Unpin> as the concrete type returned from the Acceptor or introduce an Either<IdleTimeout<TcpStream>, TcpStream> type. I can do that in a follow-up.